This invention relates to resinous copolymers. In one aspect, this invention relates to a novel polymerization process for the production of polymodal resinous block copolymers with improved melt strength properties.
Resinous block copolymers have been produced by methods employing various sequential polymerization steps. Among the pioneer inventions in the field of resinous block copolymers are such patents as U.S. Pat. No. 3,639,517 to Kitchen and Szalla, U.S. Pat. No. 4,080,407 to Fodor, and U.S. Pat. No. 4,091,053 to Kitchen.
Much effort has been directed to the preparation of substantially transparent block copolymer resins with a variety of block structures produced by a variety of monomer addition sequences and a variety of coupling agents.
One of the more important applications for substantially transparent block copolymer resins is in the packaging and related industries where there is a need for thermoplastic polymers suitable for use in conventional injection and blow molding and in other methods of forming plastics into containers, tubes, film and the like. For applications which require blow molding of the thermoplastic resin it is important that the parison have sufficient melt strength to support itself when blow molding larger parts. Better melt strength is normally associated with low melt flow; however, melt flow must be high enough to maintain processability.